Thin-film solar cells on glass substrates are likely to have a bright future due to the potentially low costs and the short energy payback times. Polycrystalline silicon (poly-Si, grain size &gt 1 pm) has the advantage of being non-toxic, abundant, and long-term stable. Glass as a substrate, however, limits the processing temperatures to ~600??C for longer process steps. Films with large grain size can be achieved by solid phase crystallisation (SPC), and especially by solid phase epitaxy (SPE) on seed layers, using amorphous silicon deposited at low temperatures as a precursor film. With SPC and SPE, the amorphous silicon film is typically crystallised at ~600??C over hours. During this anneal at atmospheric pressure -depending on the properties of the amorphous silicon film- ambient gas can percolate the film and can negatively affect the crystallisation. In this work, a high-vacuum anneal chamber was designed and built to allow the in-situ crystallisation of amorphous silicon films deposited on glass in a PECVD cluster tool. An important aspect of the design was the comfortable and safe operation of the vacuum anneal chamber to enable unattended operation. This was realised by means of a state-of-the-art, programmable temperature controller and a control circuit design that incorporates various safety interlocks. The chamber interior was optimised such that a temperature uniformity of 2-3K across the sample area was achieved. The chamber was calibrated and tested, and SPC and SPE samples were successfully crystallised. In initial SPC crystallisation experiments with solar cell structures, after post-deposition treatments, a 1 -sun open-circuit voltage of 465 mV was obtained, similar to furnace-annealed samples. In initial experiments with SPE solar cell structures, difficulties regarding the characterisation of the unmetallised solar cells with the quasi-steady-state open-circuit voltage method (QSSVOC) were encountered after post-deposition hydrogen treatment. A possible explanation for these difficulties is the contact formation with the metal probes. Furthermore, limiting factors of the QSSVOC method for the characterisation of unmetallised cells with high contact resistance values were investigated and, additionally, the accuracyof the QSSVOC setup was improved in the low light intensity range.

The roles of hydrogen induced defects in pure ZnO has been studied extensively. However, in a transition metal, such as Co, doped ZnO thin films the effect of hydrogen in electric conduction and magnetic coupling is still unclear and needs further study. Recently model predicts that hydrogen can be a shallow donor as well as an agent to induce ferromagnetism coupling between two adjacent Co ions which substitute the Zn sites at room temperature in a ZnO sample with a high Co doping ratio. However, the experimental supports is rare. In this study, Co-doped(5%) ZnO films are grown by a RF-magnetron sputtering system on glass substrate at room temperature. The growth condition is fixed for RF power in 200W, working press of 70 mtorr and various mixing ratio of H2/Ar+H2 gas. The crystal structure, electric and optical properties and the influence of vacuum annealing on the samples are studied. In this research, we found that the doping of hydrogen in Co-doped ZnO thin films truly increases the electric conductivity which is proportional to the H2/(Ar+H2) ratio. When the ratio of hydrogen is low, the (002) peak taken by a Glazing Angle X-ray Diffractometer dominates, while increasing hydrogen ratio other diffraction peaks appear, indicating an enhancement of crystal structure in all directions, and grain sizes and unit cell volume decrease. From the optical transmittance measurement, it is found that the color of films turned into metallic like and the optical band gap increases linearly with H2 ratio which can be attributed to the Burstein-Moss effect that corresponds to the increasing of carriers in the conduction band by doping of H2. The transmittance data provides the information of the ratio of crystalline and amorphous, which can also be correlated to the AFM results. When the H2 ratio is higher than 30%, more crystals and larger sizes of grains were formed in the films, such that carriers did not need to pass grain boundaries so frequently and experienced less scattering that was actually improve the electric conductivity. The electric conductivity can be even improved by post annealing in H2 environment. Moreover, the Magnetic circular dichroism (MCD) measurement shows that the Co2+ ions does truly substitute on Zn sited in Td symmetry during thin film deposition. The resistance measurement as a function of temperature found the hydrogenated Co-doped thin films are semiconductor conductive. More works are needed to determine the magnetization, identify second phases and Vo by SQUID and X-ray photoelectron spectroscopy.

Thin-film solar cells on glass substrates are likely to have a bright future due to the potentially low costs and the short energy payback times. Polycrystalline silicon (poly-Si, grain size &gt 1 pm) has the advantage of being non-toxic, abundant, and long-term stable. Glass as a substrate, however, limits the processing temperatures to ~600??C for longer process steps. Films with large grain size can be achieved by solid phase crystallisation (SPC), and especially by solid phase epitaxy (SPE) on seed layers, using amorphous silicon deposited at low temperatures as a precursor film. With SPC and SPE, the amorphous silicon film is typically crystallised at ~600??C over hours. During this anneal at atmospheric pressure -depending on the properties of the amorphous silicon film- ambient gas can percolate the film and can negatively affect the crystallisation. In this work, a high-vacuum anneal chamber was designed and built to allow the in-situ crystallisation of amorphous silicon films deposited on glass in a PECVD cluster tool. An important aspect of the design was the comfortable and safe operation of the vacuum anneal chamber to enable unattended operation. This was realised by means of a state-of-the-art, programmable temperature controller and a control circuit design that incorporates various safety interlocks. The chamber interior was optimised such that a temperature uniformity of 2-3K across the sample area was achieved. The chamber was calibrated and tested, and SPC and SPE samples were successfully crystallised. In initial SPC crystallisation experiments with solar cell structures, after post-deposition treatments, a 1 -sun open-circuit voltage of 465 mV was obtained, similar to furnace-annealed samples. In initial experiments with SPE solar cell structures, difficulties regarding the characterisation of the unmetallised solar cells with the quasi-steady-state open-circuit voltage method (QSSVOC) were encountered after post-deposition hydrogen treatment. A possible explanation for these difficulties is the contact formation with the metal probes. Furthermore, limiting factors of the QSSVOC method for the characterisation of unmetallised cells with high contact resistance values were investigated and, additionally, the accuracyof the QSSVOC setup was improved in the low light intensity range.

Stainless steel family grades are very famous for their combined corrosion resistance and high mechanical properties. These properties can be improved further by decreasing the content of impurities like carbon and oxygen. The main purpose of this research work is to study the possibility of stainless steel powder decarburization by vacuum annealing. The influence of different process parameters like treatment time, temperature, fraction size and depth of the powder layer on the decarburization process was analyzed. The investigation results showed that it is possible to achieve extra low values of carbon and oxygen in steel powder by processing it with optimum process parameters.

Graphene, a two-dimensional counterpart of three-dimensional graphite, has attracted significant interest, due to its distinctive electrical and mechanical properties, for developing electronic, optoelectronic, and sensor technologies. In general, doping of graphene is important, as it gives rise to p-type and n-type materials, and it adjusts the work function of the graphene. This adjustment is necessary in order to control charge injection and collection in devices such as solar cells and light emitting devices. Current methods for graphene doping involve high temperature process or interactions with chemicals that are not stable. Moreover, the process of transferring graphene from its growth substrate and its exposure to the environment results in a host of chemical groups that can become attached to the film and alter its electronic properties by accepting or donating electrons/holes. Intentional and controllable doping of the graphene, however, requires a deeper understanding of the impact of these groups. The proposed research will attempt to clarify the unintentional doping mechanism in graphene through adsorption or desorption of gas/vapor molecules found in standard environments. A low temperature, controllable and defect-free method for doping graphene layers will also be studied through modifying the interface of graphene and its support substrate with self-assembled monolayers (SAMs) which changes the work function and charge carriers in the graphene layer. Furthermore, current methods of chemical vapor deposition synthesis of graphene requires the film to be transferred onto a second substrate when the metal layer used for growth is not compatible with device fabrication or operation. To address this issue, the proposed work will investigate a new method for wafer scale, transfer-free synthesis of graphene on dielectric substrates using new carbon sources. This technique allows patterned synthesis on the target substrate and is compatible with standard device fabrication technologies; hence, it opens a new pathway for low cost, large area synthesis of graphene films.

The formation of the micro- and nanodomain structures during polarization reversal has been studied in single crystal lithium niobate with inhomogeneously modified conductivity. It is well known that the vacuum annealing and plasma-source ion irradiation of the lithium niobate crystals leads to sufficient increase of the bulk conductivity due to out-diffusion of the oxygen from the sample surface. Creation of layers with modified conductivity leads to inhomogeneous distribution of applied electric field in bulk of ferroelectric crystals. Polarization reversal in such a crystals permits to localize charged domain walls in the bulk. Methods of creation of charged domain walls can be used for the construction of the waveguide structures, optical modulators and resonators. The main conclusions of the work: 1) It was shown that plasma-source ion irradiation and vacuum annealing leads to inhomogeneous change of absorption and increase of the conductivity, which can be attributed to the out-diffusion of oxygen and lithium segregation in the surface layer of crystal. 2) Inhomogeneous distribution of electric field in the bulk of modified crystals leads to significant decrease of switched layer thickness. 3) Effect of formation and growth of non-through domains with charged domain walls has been revealed. 4) Analysis of switching current by modified Kolmogorov-Avraami formula permit to determine mobility of domain wall and threshold filed of polarization reversal. / Целью работы являлось экспериментальное исследование формирования микро- и нанодоменных структур в монокристаллах ниобата лития с неоднородно модифицированной проводимостью. Известно, что обработка воздействием низкоэнергетичного ионно-плазменного облучения и восстановительного отжига приводит к резкому увеличению проводимости кристаллов за счёт аут-диффузии кислорода с поверхности. Создание слоёв с измененной проводимостью приводит к неоднородному распределению электрического поля в объёме сегнетоэлектрических кристаллов, что позволяет создавать внутри-объёмные заряженные доменные структуры при переключении поляризации. Методы создания заряженных доменных структур используются для создания элементов интегральных оптических устройств: волноводных структур, оптических модуляторов и резонаторов. Основные выводы работы: 1) Показано, что ионно-плазменное облучение и восстановительный отжиг кристаллов приводят к неоднородному изменению поглощения и увеличению проводимости, что может быть отнесено за счёт аут-диффузии кислорода и сегрегации лития в поверхностном слое. 2) Установлено, что неоднородное распределение электрического поля в объёме модифицированных кристаллов приводит к значительному понижению порогового поля переключения поляризации, за счёт уменьшения толщины переключаемого слоя. 3) Впервые обнаружен и изучен эффект формирования и роста несквозных доменов с заряженными доменными стенками. 4) Анализ тока переключения модифицированной формулой Колмогорова-Аврами позволил определить подвижность доменной стенки и пороговое поле начала переключения.